Transparent conductive electrodes comprising merged metal nanowires, their structure design, and method of making such structures

ABSTRACT

A method for making a nanowire-based electrode having homogenous optical property and heterogeneous electrical property is disclosed. The method comprises coating a first solution comprising a first material on to the substrate to form a layer of nanowire network; evaporating to remove the solvent in the metal nanowire film; printing a second solution comprising a chemical reagent on top of the formed metal nanowire network layer; and oxidizing the first material into a second material by the chemical reagent, wherein the first material and second material has a refractive index difference less than 0.05 and second material is less conductive than the first material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplications 61809224, 61809353, and 61809354, US utility application13906330, and Chinese patent application 201310152173.0. The subjectmatter as set forth in each one of the following US utility patentapplications and Chinese patent application are incorporated herein byreference in its entirety:

-   Ser. No. 61/809,224, filed Apr. 5, 2013;-   Ser. No. 61/809,353, filed Apr. 6, 2013;-   Ser. No. 61/809,354, filed Apr. 6, 2013;-   Ser. No. 13/906,330, filed may 30, 2013 and-   Chinese application in 201310152173.0, file Apr. 27, 2013.

BACKGROUND

1. Technical Field

This disclosure is related to a patterned transparent conductive filmhaving homogeneous optical properties but heterogeneous electricalproperties, and method of making the same.

2. Description of the Related Art

Optically clear and electrically conductive films made from metalnanowires are promising replacement for ITO films, which are used invarious electronics devices such as LCDs, OLEDs and Solar cells.

Transparent conductive films in the display and touch screen devices,requiring the films to be patterned to have conductive regions andnon-conductive regions, while maintaining the optical transparency.Previously, when a transparent conductive film consisting of a mesh ofsilver nanowires embedded into a film of substrate or bound on thesubstrate surface by an adhesive layer is patterned, the differencebetween the optical properties of the conductive regions (containingsilver nanowire) and the non-conductive regions of the film becomevisible to the human eye.

A method to patterning a film having invisible edges between conductiveand non-conductive areas is needed. One solution is to make a conductivefilm having identical optical properties in both conductive andnon-conductive regions. In addition, the process of making such apatterned film should be easy to operate, scalable, and robust.

SUMMARY OF THE INVENTION

It is the object of the present invention, to provide transparentconductive film having desirable electrical and optical properties,adaptable to any substrates, and can be manufactured and patterned in alow-cost, high-throughput process.

In one aspect of the present invention, it discloses conductive filmcompositions having homogenous optical properties and heterogeneouselectrical properties.

In one embodiment, the present invention is directed to a conductivefilm composition having homogenous optical property and heterogeneouselectrical property. Said film comprises a first region comprising afirst material;

-   -   a second region, comprising a second material;    -   wherein the refractive index difference between first material        and the second material is less than 0.2, and the haze        difference is less than 0.2, the second material is an oxidation        form of the first material and the second region is less        conductive than the first region.

In another embodiment, it is described herein a patterned transparentconductive film, comprising a substrate;

-   -   a substantial single layer on top of the substrate, comprising    -   a first region comprising a network of metal nanowires; and    -   a second region, comprising a metal/metal oxide nanowire in a        core shell structure, wherein the core of the nanowire comprise        element metal and the shell of the nanowire comprise metal        oxide.

In a further embodiment, it is described herein a patterned transparentconductive film, comprising

-   -   a substrate;    -   a substantial single layer on top of the substrate, comprising    -   a first region comprising a network of metal nanowires; and    -   a second region, comprising at least one nanowire having a        junction connected to another nanowire but electrically        non-conductive,    -   wherein the junction comprises metal oxides and    -   wherein the total thickness of the single layer is about 150 nm        or less and the second region has one dimension is 5-200 um.

In still a further embodiment, a conductive electrode composition havinghomogenous optical property and heterogeneous electrical property,comprising

-   -   a first region, comprising a first material;    -   a second region, comprising a second material;    -   wherein the refractive index differences between the first and        second material is less than 0.2, and a haze difference no more        than 0.2%, one dimension of the first region is at least 10 um,        the first material is converted to the second material by UV        light and photo acid generator and the first region is more        conductive than the second region.

In yet another embodiment, it is described herein a patternedtransparent conductive film, comprising

-   -   a substrate;    -   a substantial single layer on top of the substrate, comprising    -   a first region comprising a network of silver nanowires and        surface functionalization means for protecting the nanowire from        surface oxidation; and    -   a second region, comprising a plurality of silver nanowires.

In another aspect of the present invention, it discloses severaldifferent methods to make conductive film compositions having homogenousoptical properties and heterogeneous electrical properties.

In one embodiment, the present invention provides a method for making ananowire-based film having homogenous optical property and heterogeneouselectrical property. The method to making a nanowire based conductivefilm comprises

-   -   1) providing a substrate,    -   2) coating a first solution comprising a first material on to        the substrate to form a layer of nanowire network;    -   3) evaporating to remove the solvent in the metal nanowire film;    -   4) printing a second solution comprising a chemical reagent on        top of the formed metal nanowire network layer, in a        pre-determined pattern;    -   5) heating and drying to remove the solvent in the second        solution; and    -   6) converting the first material into a second material by the        chemical reagent, wherein the first material and second material        has a refractive index difference less than 0.05 and second        material is less conductive than the first material.

The method step converting the first material into a second material bythe chemical reagent, further comprises radiating UV light without usinga patterned mask.

The method step converting the first material into a second material bythe chemical reagent, further comprises applying heat to the area wherethe second solution is deposited.

In a further embodiment, the present invention is directed to a novelmethod to pattern a transparent conductive film. The method ofpatterning the conductive film comprising

-   -   providing a substrate,    -   coating a first solution comprising a first material and a photo        acid generator or photosensitive materials on to the substrate        to form a layer of nanowire film;    -   evaporating away the solvent in the metal nanowire film;    -   positioning a mask above the metal nanowire film, wherein the        mask has some areas permitting UV light to pass through and some        areas shielding UV light away from the nanowire film;    -   shining UV light above the mask;    -   converting the first material into a second material by the        photo acid generator and UV light, wherein the first material        and second material has a refractive index difference less than        0.2 and a haze difference less than 0.2% second material is less        conductive than the first material; and    -   annealing the film and removing the unreacted photo acid        generator in the area shielded by the mask.

The method to patterning an conductive film comprising

providing a substrate,forming a film comprising a first region having metal nanowires, whereinat least some of metal nanowires are surface functionalized and areinert to oxidation or acid reaction;evaporating away the solvent in the metal nanowire film;exposing the nanowire film to a chemical reagent;converting the metal in the metal nanowire network to its oxidativestate and forming a second region,wherein the first and second region have different electricalproperties, but having substantially same or similar optical properties,with difference in refractive indexes less than 0.2, and difference inhaze no more than 0.2%.

BRIEF DESCRIPTION OF THE FIGURES

The invention and the detailed description thereof may be understood byreference to the following figures:

FIG. 1 is an exemplary nanowire, having a diameter of d and length L;

FIGS. 2 a-e are schematic illustrations of cross section views ofdifferent nanowires in accordance with the aspects of the presentinvention;

FIG. 3 is a schematic diagram of a single layer conductive film, inaccordance with the aspects in the present invention;

FIG. 4 a is a cross-section diagram of an exemplary metal nanowirenetwork on the substrate;

FIGS. 4 b and c are illustrations of the cross sections of the filmswhen a second solution is printed onto the substrate and nanowirenetwork;

FIG. 4 d is an illustration of the cross section of the film after thesecond solution reacted into the nanowire network.

FIG. 5 a is a cross-section diagram of an exemplary metal nanowirenetwork on the substrate;

FIG. 5 b is an illustration of the cross section of the film when a maskis positioned above the substrate and nanowire network;

FIG. 5 c-d are illustrations of the cross section of the film after theUV radiation.

FIG. 6 a is an illustration of an exemplary metal nanowire;

FIG. 6 b is an illustration of an exemplary metal nanowire after acid oroxidant exposure;

FIG. 6 c is an illustration of the composition of another exemplarymetal nanowire in the conductive film; and

FIG. 6 d is an illustration of the composition of another exemplarymetal nanowire in the conductive film after the reaction with acid oroxidation.

FIG. 7 a is an illustration of an exemplary metal nanowire having selfassembly monolayer for protecting metal nanowire from surfaceoxidization;

FIG. 7 b is an illustration of an exemplary metal nanowire after acid oroxidant exposure;

FIG. 8 a is an illustration of the composition of another exemplarymetal nanowire having self assembly monolayer in the conductive filmfilm;

FIG. 8 b is an illustration of the composition of another exemplarymetal nanowire in the conductive film after the reaction with acid oroxidation;

FIGS. 9 a-b are cross sectional SEM images of a transparent conductiveelectrode comprising surface functionalized metal nanowires;

FIG. 10 illustrates an exemplary patterns for inkjet printing, whereinthe white lines represent where the printing lines of the etchant;

FIG. 11 shows an SEM image of a comparative example, wherein the secondregions were all etched away;

FIG. 12 shows an SEM image wherein the second region is oxidized insteadof all etched way;

FIG. 13 a is an SEM image showing the conductive film comprising surfacefunctionalize metal nanowires after being patterned; and

FIG. 13 b is a zoomed-in image of part of FIG. 13 a.

DETAILED DESCRIPTION OF SELECTED EXAMPLES

Hereinafter, selected examples of methods for making a transparentconductive films will be discussed in the following with reference tothe accompanying drawings. It will be appreciated by those skilled inthe art that the following discussion is for illustration purposes, andshould not be interpreted as a limitation. Other variances within thescope of this disclosure are also applicable.

General Description

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.

In the scope of the present invention, printing, wet coating and alikeare all referred to the general category of a wet coating method,including inkjet printing, spray printing, nozzle printing, gravureprinting, screening printing, etc. Printing and coating can be usedinterchangeably.

Nanowires

In accordance with the aspects with the present invention, nanowire 100have a cylindrical shape, having a diameter d and length L as shown inFIG. 1. The aspect ratios of nanowires are L/d. Suitable aspect ratiosof the nanowires are between 100 to 100,000. In one preferred example,the aspect ratios of the nanowires are more than 1000, in order toprovide a transparent conductive film, because longer and thinnernanowires may enable more efficient conductive networks while permittinglower overall density of wires for achieving a higher transparency.

Metal Nanowires

As known in the art, conductive nanowires include metal nanowires andnon-metallic nano-wires. In general, “metal nanowire” refers to ametallic wire comprising element metal and metal alloys. Non-metallicnanowires include, for example, carbon nanotubes (CNTs), conductivepolymer fibers and the like.

In accordance with the aspects of the present invention, metal nanowiresrefers to substantially elemental metal and metal alloys. Optionally,the metal nano-wires may have less than 5-10% (by moles) of metaloxides. Metal oxides may exist in the metal nanowire shell or core as animpurity or defect in the nanowire synthesis. FIGS. 2 a-e are schematicillustrations of cross section views of different nanowires inaccordance with the aspects of the present invention, wherein element200 is an elemental silver and element 202 is an oxidative state ofsilver.

In accordance with the aspects of the present invention, metal oxidenanowires refers to the nanowires are substantially metal oxides.Optionally, metal oxide nanowires may have less than 5-10% (by moles) ofelemental metal, due to incomplete oxidation or any other reasons.

In accordance with the aspects of the present invention, hybridnanowires are metal/metal oxide nanowires, wherein the nanowires, havingboth elemental metal and metal oxides as major components. Metal/metaloxide hybrid nanowires may comprise 40% (mole %) metal oxide and 60%(mole %) elemental metal. Metal/metal oxide hybrid nanowires maycomprise 60% (mole %) metal oxide and 40% (mole %) elemental metal.

The diameters of the metal nanowires, metal oxide nanowires, or hybridnanowires are less than 200 nm, and less than 100 nm, and morepreferably less than 50 nm.

Suitable elemental metal employed in nanowires can be based on anymetal, including without limitation, silver, gold, copper, nickel, andgold-plated silver. In one example, silver nanowires are used to makethe conductive electrode film because of the small refractive indexdifference between elemental silver and silver oxide.

Optionally, the metal nanowires, metal oxide nanowires and hybridnanowires, further comprises other minor component, for example, but notlimited to, seeding element from the nanowire synthesis.

FIGS. 2 a-e are schematic illustrations of the cross section views ofdifferent nanowires. FIG. 2 a is an exemplar metal nanowire, whereinelement 200 is a cross section of silver nanowire. FIG. 2 b is anexemplar metal/metal oxide hybrid nanowire, wherein the metal oxide andmetal are arranged in a core shell structure, having metal nanowire formthe core and metal oxide become the shell wrapping around the core. FIG.2 c is an exemplar metal/metal oxide hybrid nanowire, wherein the metaloxide and metal are arranged in a pseudo core shell structure, whereinthe “core” has more elemental metal than the metal oxide and the “shell”has more metal oxide than elemental metal. In one example, FIG. 2 coccurs as the result of an oxidation reaction on a metal nanowire,wherein only the exposed elemental are oxidized and the surface of themetal nanowire does not get exposed equally to the oxidative reagent orcondition. FIG. 2 d is an exemplar metal/metal oxide hybrid nanowire,wherein the metal oxide and metal are arranged randomly, but stillhaving a pattern that there are more metal oxide on the surface of thenanowire, and there is less metal inside the nanowire. FIG. 2 e is anexemplar metal oxide hybrid nano-wire, wherein both the core and shellof the nano-wire are predominantly metal oxide.

FIGS. 2 a-e are exemplar illustrations and should not be construed aslimitations. The contours of the nanowires, if are marked, it is onlyintended for clarity purposes. The interfaces and boundaries betweendifferent chemical components are either visible or not visible. It isdepends on the refractive index of the metal and metal oxide.

Optical and Electrical Characteristics of the Nanowires

Generally for a single nanowire, its resistivity is based on itsdiameter. The larger the diameter of the nanowire, the smaller theresistivity or it is more conductive. However, the larger the diameterof the nanowire, it blocks more light and become less transparent.Therefore an optimal diameter range is desired in order to achieve bothhighly conductive and highly transparent metal nanowires.

In addition, in order for a metal nanowire to be conductive across asubstrate either laterally or horizontally, the single metal nanowire(s) needs to 1) extends through a region or to 2) be connected to anumber of other nanowires. Therefore the longer the single nanowirelength, in principle the longer the conductive pathway. In typicalexamples of the present invention, an aspect ratio above 1000 isdesired.

Conductive Film

In accordance with the aspects of the present invention, when aplurality of nanowires is deposited onto a substrate to make aconductive film, the film formed is substantially a single layer. In theconductive film, the nanowires are arranged at least above a minimalconcentration, so called percolation threshold, so that the nanowiresare not spaced too far apart from each other to form a conductivepathway.

When a plurality of single nanowires is networked together to form amultiple interconnected conductive pathways, said plurality of thenanowires is referred to as clusters. When two or more nanowire clustersare networked together, a conductive layer or film is formed. Inaccordance with the aspect of the present invention, nanowire dustershas size of less than 200 nm in one dimension, more typically less than100 or 50 nm in one dimension.

As used herein, “a single layer” or “a substantial single layer” isgenerally less than 150 nm, which is about three-nanowire thickness.More typically, “a single layer” or “a substantial single layer” isgenerally less than 100 nm, two-nanowire thickness. Preferably, “asingle layer” or “a substantial single layer” is generally 50 nm orless, one nanowire thickness. In various embodiments, the thickness ofthe nano-clusters are in the range of 10 to 0.40 nm, 20 to 40 nm, 5 to20 nm, 10 to 30 nm, 40 to 60 nm, 50 to 70 nm.

The clusters are formed by nanowires isotropically or anisotropicaily.The nanoclusters can also have a pseudo diameter, pseudo length andpseudo aspect ratio. Lengthwise, anisotropic nanoclusters (e.g., aplurality networked nanowires, pseudo aspect ratio does not equal toone) are more than 500 nm, or more than 1 μm, or more than 10 μm inlength. In various embodiments, the lengths of the nanoclusters are inthe range of 5 to 30 μm, or in the range of 15 to 50 μm, 25 to 75 μm, 30to 60 μm, 40 to 80 μm, or 50 to 100 μm.

In accordance with the aspects of the present invention, when theconductive film is patterned into conductive regions and non-conductiveregions, conductive regions comprise interconnected or networkednanoclusters, whereas the non-conductive region comprise segregated orisolate nanoclusters.

In accordance with the aspects of the present invention, when the metalnanowire is silver nanowire, one silver nanowire is present in ananocluster. In one example, said silver within the nanocluster isoxidized into a silver oxide nanowire. The interruption in theconductive pathway turned connected nanoclusters into isolatednanolusters, which further turning a region from conductive region intoa nonconductive region.

The conductive films described herein, are having conductive regions andnon conductive regions. Conductive regions and nonconductive regions aretogether referred as patterns in the conductive film. In accordance withaspects of the present invention, in one embodiment, the nonconductiveregions are formed from the conductive regions through oxidation, photooxidation reaction or even fragmentation reactions. As a result, thenonconductive regions comprise nanowires having metals in the oxidativestates and metal nanowires are shorter in length than that of conductiveregions (parent). The conductive regions typically comprise metalnano-wires having high aspect ratios. Optionally, the conductive regionmay further comprise metal nanowires having surface functionalizationmeans, protecting the metal nanowires from undergo undesired oxidation,photo-oxidation or fragmentation.

In view of the foregoing discussion, the present invention disclosespatterned conductive films with excellent optical properties, electricalproperties and mechanical properties. The patterned transparentconductive films disclosed herein have an optical transmittance higherthan 90%, a haze value less than 2%, and typically less than 1%, whilemaintaining the sheet resistance lower than 100 Ohms/sq and typicallyless than 50 Ohms/sq.

Super Long and Thin Nanowires

The patterned conductive film in the present invention comprises asubstrate, and a substantially single layer of conductive materialsdeposited on top of the substrate. The single layer conductive materialcomprises one or more metal nanowires. Longer and thinner thanconventional metal nanowires are employed in the film to achieve hightransparency, low haze and high conductivity in the conductive regionand high resolution in the patterned conductive film.

In one embodiment of the present invention, the patterned transparentconductive film comprises nanowires having a longer than usual lengthand thinner than usual diameters. The usual length is defined as about10-20 micrometers in length and the usual diameters are defined as about50-100 nm in diameters in the scope of the present invention.

Transparent conductive films in the art typically employing metalnanowires having diameters around 50-100 nm, with 10-20 micrometers inlength. The patterned transparent conductive films disclosed in thepresent invention, comprises metal nanowires are less than 50 nm indiameters and longer than about 20-100 micrometers. In one preferredexample of the present invention, the patterned transparent conductivefilm comprises nanowires having less than 30 nm in diameters. The longerand thinner metal nanowires significantly reduces the amount of lightscattering and the contrast between the areas having nanowires and theareas without, leading to a conductive film with lower haze. Inaddition, the longer than usual nanowires further facilitates theelectron transport within the conductive region of the film, leading toimproved electrical conductivity and reduced sheet resistance. In theexamples of the present invention, the patterned transparent filmcomprises metal nanowires having less than 50 nm in diameters and 20-100micrometers in length, have an optical transmittance higher than 90%, ahaze value less than 0.6%, while maintaining the sheet resistance lowerthan 50 Ohms/sq.

The unusual long and unusual thin metal nanowires can be made by atwo-step synthesis method. Apart from the conventional one step processof making metal nanowires in the art, which typically lead to metalnanowires 80-100 nm in diameters and 20-30 micrometers in length, themethod disclosed in the present invention comprises a two-step process.A first step is a proceeding step, forming most of the nanowirenucleation seeds. A second step is a growing step, where the nucleationseeds grow preferentially in one dimension in a controlled manner.Further, the nucleation seeds can be purified before being used in thegrowing step. Subsequently, the metal nanowires collected after thegrowing step can be further purified to have nanowires with evennarrower distribution in length and diameters. Comparing theconventional one step method, the two-step process has two advantages.First, the proceeding step incubates the formation of the nucleationseed, which significantly reduces the concentration of the nanowire“growing centers”. Second, the growing step is conditioned that theprecursors are continuously growing in one predetermined direction inlength, thus reducing the formation of junctions and branches in themetal nanowire network.

Substrate

In accordance with the aspects of the present invention, substraterefers to a material onto which the conductive layer is coated on topof. The substrate can be either rigid or flexible. The substrate ispreferred to be highly transparent in the visible wavelength. Exemplarrigid substrates include, glass, polycarbonates, particularly highrefractive index polycarbonates, acrylics, and the like. Exemplarflexible substrates include, but are not limited to: polyesters (e.g.,polyethylene terephthalate (PET), polyester naphthalate (PEN), andpoly-carbonate, polyolefins (e.g., linear, branched, and cyclicpolyolefins), and other conventional polymeric films,

Properties of a the Patterned Film

Typically, the optical transparence or clarity of the conductive filmcan be quantitatively defined by parameters including light transmissionand haze. “Light transmission” refers to the percentage of an incidentlight transmitted through a medium. In various embodiments, the lighttransmission of the conductive layer is at least 90% and can be as highas 98%.

Haze is an index of light diffusion. It refers to the percentage ofquantity of light separated from the incident light and scattered duringtransmission. Unlike light transmission, which is largely a property ofthe medium, haze is often a production concern and is typically causedby surface roughness and embedded particles or compositionalheterogeneities in the medium. In various embodiments, the haze of thepatterned transparent conductive film is no more than 5% and may be aslow as no more than 2% to 0.5%.

Wet Coating Process

The transparent conductive film can be fabricated by any feasible wetcoating method, including sheet coating, web-coating, printing,spraying, gravure printing, and slot die coating, transfer printing orlamination. If the substrate is a flexible substrate, roll to rollcoating is preferred for large area and high throughput. Sheet Coatingor lamination is more suitable when the conductive film is formed on topof rigid substrate, for example glass. Both roll-to-roll or sheetcoating can be fully automated to dramatically reduces the cost offabricating transparent conductive films. All the patterning methodsdescribed herein, can be run on a fully integrated line, or serially inparallel processes.

Composition 1

As an illustrative example, FIG. 3 shows a patterned transparentconductive film comprising a substrate and a substantial single layercoated on the substrate. The single layer comprises a plurality of metalnanowires. The metal nanowires form a conductive network. The filmcomprises a first region and second region, which is not shown from thiscross sectional view.

The present invention is directed to a composition and method ofmanufacturing nanowire based conductive film. Said nanowire based filmhas a pattern invisible to the human eye. Invisible to the human eyemeans the interface between the regions in the patterned conductive filmis not visible when observing under the visible light.

The present invention is directed to a composition and method ofmanufacturing a nanowire based conductive film. The film comprises afirst region comprising a first material and a second region comprisinga second material, wherein the difference of refractive index betweenthe first and second region is less than 0.05.

The present invention is directed to a composition and method ofmanufacturing a nanowire based conductive film. The film comprises afirst region comprising a first material and a second region comprisinga second material, wherein at least one dimension of the second regionis less than 10 um. Optionally, one dimension of the second region islonger than 50 um. Optionally, one dimension of the second region lessthan 5-10 um.

The present invention is directed to a composition and method ofmanufacturing a nanowire based conductive film. The film comprises afirst region comprising a first material and a second region comprisinga second material, wherein the distance between one first region toanother first region is longer than 5 um. Optionally, the distancebetween one first region to another first region is longer than 10 um.

The pattern comprises electrical conductive regions and electricalnon-conductive regions. The refractive index difference between theelectrical conductive region and electrical non-conductive regions isless than 0.2. The transmittance difference between the electricalconductive region and electrical non-conductive regions is less than0.2. The haze differences between the electrical conductive region andelectrical non-conductive regions is less than 0.3-0.5. The sheetresistance of electrical conductive regions are less than 300 Ω/sq. Thesheet resistance of electrical non-conductive regions are more than 1000Ω/sq.

The pattern comprises electrical conductive regions and electricalnon-conductive regions. The conductive region is converted into thenon-conductive regions by an oxidation reaction.

In one example of the present invention, the first region of the filmcomprises silver nanowire. Upon reaction with a chemical solution,silver is converted into silver oxide, which forms the second region.The refractive index of the film containing silver metal is 1.6 and therefractive index of the film containing silver oxide is 1.59. Therefractive index difference between the film containing silver metal andthe film containing silver oxide is 0.01. The chemical solution isanything capable of oxidizing silver into silver metal, for example anoxidizing agent solution. The silver is the sole or primary conductivematerial for the conductive region and silver oxide is the sole orprimary converted material for the non-conductive region.

In a further example, when the silver nanowire is oxidized to form thesecond region, it forms a silver oxide/silver hybrid nanowire (FIG. 2a-e). In one instance of the present example, the silver oxide/silver isarranged in a core shell structure, wherein silver nanowire is the core,and the silver oxide forms the shell coating over the silver nanowirecore. In another instance of the present invention, the silveroxide/silver is arranged in a pseudo core shell structure, wherein thesurface of the hybrid nanowire has more silver oxide than silver, andthe core of the hybrid nanowire has more elemental silver than silveroxide. In still another instance of the present invention, the silveroxide is formed randomly in the silver nanowire. In yet anotherinstance, when silver is oxidized into silver oxide to form the secondregion, it oxidation undergo to the completion and yield silver oxidenanowire.

In one example of the present invention, the first region of the filmcomprises silver nanowire. Upon reaction with a chemical solution,silver is converted into a silver salt. Examples of the silver saltincludes silver halides, silver nitrate and silver sulfate, and thelike. The refractive index of the film containing silver metal is 1.6and the refractive index of the film containing silver oxide is 1.59.The refractive index difference between the film containing silver metaland the film containing silver oxide is 0.01. The chemical solution isanything capable of oxidizing silver into silver metal, for example anacid solution. The silver is the sole or primary conductive material forthe conductive region and silver oxide is the sole or primary convertedmaterial for the non-conductive region.

The first region, an electrical conductive region, and the secondregion, a non-electrical conductive region, as formed based on thedisclosure herein, has a conductivity ratio of the conductive regionover non conductive region more than 1000, and wherein the conductiveregion and the non conductive region are optically uniform.

Methods 1-3

A patterned conductive film can be formed by selectively oxidizing thenanowire region. The oxidizing agent can be placed onto the conductivefilm after the film of metal nanowire is formed. Alternative, theoxidizing agent can be mixed into the nanowire ink and made into thenanowire film.

The curing process can be carried out photolytically or thermally. FIGS.4 a-d illustrates an embodiment in which a conductive layer isthermally-patterned. FIGS. 5 a-d and 6 a-d illustrates an embodiment inwhich a conductive layer is photolytically patterned.

In some embodiments, thermal-patterning can be carried out using aninsulating thermal mask (e.g., an aperture mask), which only exposesregions to be converted to a heat source.

In other embodiments, photolytically patterning can be achieved by usinga mask. In such a process, the mask provides areas of openings and areasof shadows, wherein the openings permits the UV through to convert themetal nanowires to metal oxides while the shadows protecting the metalnanowire in the conductive region to be oxidized.

Alternatively, both thermal-patterning or photolytically patterning canbe achieve using a mask-less approach. In a mask-less approach, theoxidizing agent is directly-written onto the layer or film of metalnanowire in a predetermined pattern. Applying heat or UV radiationthroughout the film can only create oxidation reaction in the areaswhere the oxidizing chemicals are deposited, thus leading to thepredetermined patterns.

Both the photo-patterning method and thermal-patterning method arecompatible with wet coating process described, which are easily scalableto large areas of substrates and offers low cost high throughputmanufacturing.

The present invention provides a method to make patterned transparentconductive film. The patterned transparent film comprises two regions, afirst region, a conductive region and a second region, non-conductiveregion, wherein the first region is converted to a second region by anoxidation reaction.

First, a substrate is cleaned and a first solution comprising metalnanowires, preferably silver nanowires are coated onto the substrate.After drying to remove the solvent, a film of metal nanowire network 102is formed.

Referring to FIG. 4 b, then a second solution 104 is printed ontosurface of the nanowire film 102 in designated areas. Depends on theresolution and throughput requirement, various printing method can beused to deliver the second solution to the surface of the nanowire film.In one example, ink jet printing is used and distance between oneconductive region to another conductive region is at least 5 um. Inanother example, screen printing is used and distance between oneconductive region to another conductive region is at least 50 um. Inanother example, gravure printing is used and distance between oneconductive region to another is at least 1 um. In another example, thesubstrate can first be masked with photoresist patterns and thenimmersed into a bath of the second solution. The distance between oneconductive region to another conductive region is defined by thephotoresist pattern and can be at least 0.5 um.

Upon drying, the solvent in the second solution is evaporated and thearea contacted with solution 104 is converted to 106, wherein 102 and106 has different chemical composition.

Optionally, refer to FIG. 3, before the solvent of the second solution104 is evaporated, heating is employed is facilitate the chemicaloxidation from 102 to 106.

After the removal of solution 104, 102 is converted into 106. In oneexample, 102 is a conductive region and 106 is non conductive region.102 is a film containing silver nanowire network and 106 is the filmcontaining metal oxides of the silver metal, or partially oxidizedsilver nanowires, or shorter nanowires not overlapping with each other,a less conductive or non-conductive region.

The present invention provides a method to make patterned transparentconductive film. The patterned transparent film comprises two regions, afirst region, a conductive region and a second region, non-conductiveregion, wherein the first region is converted to a second region by areduction reaction.

First, a substrate is cleaned and a first solution comprising metaloxide nanowires, preferably silver oxide nanowires or composite fiberswith silver oxide are coated onto the substrate. After drying to removethe solvent, a film of metal oxide nanowire network 102 is formed.

Referring to FIG. 4 b, then a second solution 104 is printed ontosurface of the nanowire film 102 in designated areas. Depends on theresolution and throughput requirement, various printing method can beused to deliver the second solution to the surface of the nanowire film.In one example, ink jet printing is used and distance between oneconductive region to another conductive region is at least 10 um. Inanother example, screen printing is used and distance between oneconductive region to another conductive region is at least 50 um. Inanother example, gravure printing is used and distance between oneconductive region to another is at least 1 um. In another example, thesubstrate can first be masked with photoresist patterns and thenimmersed into a bath of the second solution. The distance between oneconductive region to another conductive region is defined by thephotoresist pattern and can be at least 0.5 um.

Upon drying, the solvent in the second solution is evaporated and thearea contacted with solution 104 is converted to 106, wherein 102 and106 has different chemical composition, 102 is the oxide(s) or oxidationstate of 106.

Optionally, refer to FIG. 4 c, before the solvent of the second solution104 is evaporated, heating is employed is facilitate the chemicalreduction conversion from 102 to 106.

After the removal of solution 104, 102 is converted into 106. In oneexample, 102 is a less conductive region and 106 is a more conductiveregion. In one preferred example, the 102 is silver oxide and 106 issilver metal.

Oxidizing Agents

Oxidizing agents can be anything as long as the chemical agent is strongenough to convert elemental metal to metal oxide, particularlyconverting silver into silver oxide. In one preferred example, theoxidizing agent is a photo-acid generator. The advantage of usingphoto-acid generator over other oxidizing agent is it can be removedrelatively easily after the pattern is made. The photo-acid generatorcan be directed printed onto the nanowire surface as in FIG. 4 b, andthe followed the process illustrated in FIGS. 4 a-d to create patterns.Or the photo-acid generator can be mixed with the nanowires solution andprinted onto the substrate together as in FIG. 5 a, and the followed theprocess illustrated in FIGS. 5 a-d to create patterns. Or the photo-acidgenerator can be printed as a separate player (107) onto the nanowiresurface as in FIG. 6 b, and the followed the process illustrated inFIGS. 6 a-d to create patterns.

Example 1 of Using a Photo Acid Generator

In some embodiments, the present invention is directed to a compositionand method of manufacturing a nanowire based conductive film. The filmcomprises a first region comprising a first material and a second regioncomprising a second material. In some examples, the second material isgenerated from the first material by a combination of UV light and photoacid generator.

In one example of the present invention, the first region of the filmcomprises silver nanowire and at least one photosensitive compound. Uponirradiation with UV light, the photosensitive compound degrades togenerate acid, which converts silver into silver oxide. The refractiveindex of first region containing silver metal is 1.6 and the refractiveindex of the silver oxide is 1.59. The refractive index differencebetween the silver metal and silver oxide is 0.01.

The present invention provides a method to make patterned transparentconductive film. The patterned transparent film comprises two regions, afirst region, a conductive region and a second region, less-conductiveor non-conductive region, wherein the first region is converted to asecond region by a photo oxidation reaction.

First, a substrate is cleaned and a first solution comprising metalnanowires, preferably silver nanowires, together with at least one photoacid generator, are coated onto the substrate. After drying to removethe solvent, a film of metal nanowire network 103 comprising photo acidgenerator is formed.

Referring to FIG. 5 b, then a mask 105 is then positioned above thesurface of the nanowire film 103. The mask has designated openings,allowing UV light to pass through.

Upon UV radiation, referring to FIG. 5 c, the photo acid generator, inthe area exposed to the UV light, is activated, converting the metalnanowire into the corresponding metal oxide.

After the oxidation reaction, heating the film decompose unreacted photoacid generator as shown in FIG. 5 d. 103 is converted into a metalnanowire network 102. The film is absent from photo acid generator.

Example 2 of Using a Photo Acid Generator

The present invention provides a method to make patterned transparentconductive film. The patterned transparent film comprises two regions, afirst region, a conductive region and a second region, less-conductiveor non-conductive region, wherein the first region is converted to asecond region by UV radiation.

First, as shown in FIG. 6 a, a substrate is cleaned and a first solutioncomprising metal nanowires, preferably silver nanowires, are coated ontothe substrate. After drying to remove the solvent, a film of metalnanowire network 102 is formed.

Referring to FIG. 6 b, subsequently, another layer 107 comprising photoacid generator is deposited directly on top of the film 102. In the film107, photo acid generator is homogenously spread throughout the film.

Then, a mask 105 is then positioned above the surface of the layer 107.The mask has designated openings, allowing UV light to pass through. Thephoto acid generator in the area exposed to the UV light is activated,converting the metal nanowire 102 into the corresponding metal oxide106, as illustrated in FIG. 6 d.

After the oxidation reaction, unreacted photo acid generator 107 asshown in FIG. 8, is washed away or decomposed by heating. The finalproduct comprises a silver nanowire region and an oxidative product ofsilver nanowire region.

In accordance with the present invention, photo acid generator can bedeposited onto the substrate by any wet coating method. The printing,wet coating and alike are all referred to the general category of a wetcoating method, including inkjet printing, spray printing, nozzleprinting, gravure printing, screening printing, etc. Printing andcoating can be used interchangeably.

Examples of photo acid generators include, but are not limited to, thenon-ionic and ionic photoacid generators from BASF, such as Irgacure PAG103, Irgacure PAG 121, Irgacure PAG 203, CGI 725, CGI 1907, Irgacure250, Irgacure PAG 290, and GSID26-1.

In one embodiment of the present invention, the film of nanowires isfirst prepared on top of a substrate. IR laser is shined onto the filmof nanowire through a photo mask while heating. In one example, thesubstrate and the nanowire film are heated at 250 C for 10 min. Inanother example, the substrate and the nanowire film are heated at 300 Cfor 1 min. The heating temperature and time is optimized according thesize of the substrate, and other process parameters and economics.

In another embodiment of the present invention, the film of nanowire arefirst prepared on the top of the substrate. After drying, a solvent isintroduced into the nanowire network. The solvent can be introduced byink jet printing or spray coating through a mask, or a gravure printing.The solvent swells the nanowire network, changes the arrangement of themetal nanowire network by dissolving or partially dissolving the binderor other organic modifier in the film. As a result the rearrangement ofthe metal nanowires can cause isolate nanowire clusters which makes thefilm less or not conductive. Exemplar solvent includes alcohol-basedsolvents, such as isopropanol.

Method 5—Surface functionalization

To provide further resolution into patterning, the present invention isdirected to another method of manufacturing patterned nanowire basedconductive film, wherein the patterned conductive film compriseconductive regions and non conductive regions, and the conductiveregions comprise nanowires protected by surface functionalization means.Exemplar surface functionalization means are self assembly monolayers onthe metal nanowire. FIGS. 9 a and 9 b are cross sectional SEM images ofthe transparent conductive electrodes comprising surface functionalizedmetal nanowires.

In one embodiment of the present invention, it is directed to a materialcomposition of the conductive film. The conductive film comprises asubstrate; a substantially single layer on top of the substrate, whereinthe single layer comprise surface functionalized metal nanowires andnon-surface functionalized metal nanowires. The surface functionalizedmetal nanowires are chemically inert to the subsequent reaction withacid or other oxidation reagent. The non-surface functionalized metalnanowires are capable of undergoing chemical conversion when exposed toacid or other oxidative reagent.

The surface functionalized metal nanowires form a first region of thefilm. After the non-surface functionalized metal nanowires are convertedto the corresponding oxidative state to form a second region of thefilm. The first region is a conductive region and second region is aless conductive or non-conductive region. In one example, the firstregion comprises silver metal. In another example, the second regioncomprises silver salt. In still another example, the second regioncomprises silver oxide. The first region contains conductive networkwith surface functionalized metal nanowires and non-surfacefunctionalized metal nanowires. The second region comprises surfacefunctionalized metal nanowires and converted silver salts and silveroxide.

The first region and second region of the present embodiment havesubstantially same optical properties. In another words the selfassembly monolayers as surface functionalization means for the metalnanowires in the first region does not offer significant refractiveindex change. The patterned conductive film the difference in refractiveindex between the first and second region is less than 0.2, and thedifference in haze is no more than 0.2%. In one example first regioncontains silver, having a refractive index of 1.61. In another example,the second region contains silver oxide, having a refractive index of1.59.

The single layer in the patterned conductive film has surfacefunctionalized nanowires and non-surface functionalized nanowires.

In one example, the surface functionalized nanowire and non-surfacefunctionalized nanowire are the different portions of the same nanowire,as shown in FIG. 7 a. Upon oxidation or acid exposure, referring to FIG.7 b, the nanowire in FIG. 7 a can first be oxidized and then be fragmentinto two parts, having the surface functionalized portions de-attachedfrom each other. This reduces the original length of the nanowire,making the converted region less conductive. If the all the nanowires inthe converted region is fragmented, the average length of the nanowiresin the fragmented region is less than half of the original length, whichis the same average length of the first region comprising nanowireswhich are self assembly monolayer protected.

In another example, the surface functionalized nanowire and non-surfacefunctionalized nanowire are different nanowires, as shown in FIG. 8 a.Upon oxidation or acid exposure, referring to FIG. 8 b, the nanowirewithout the surface functionalization disintegrates, leaving the surfacefunctionalized nanowires maintaining its length. The surfacefunctionalized nanowire is a completely functionalized nanowire,synthesized, characterized and purified before use. A mixture ofcompletely functionalized nanowire and non-surface functionalized metalnanowire in a controlled ratio is used to prepare the nanowire film inthe patterned conductive film.

In still another example, the surface functionalized nanowire andnon-surface functionalized nanowire are both different portions of thesame nanowire as in FIG. 7 a and different nanowires, as shown in FIG. 8a. Upon oxidation or acid exposure, some nanowires disintegrates,reducing in length but some keeping its original length. The mixture ofthe nanowire can be an average or statistical mixture of thefunctionalized nanowire and non-surface functionalized metal nanowires.

The present invention is directed to a method of manufacturing apatterned nanowire based conductive film. The film comprises a firstregion comprising functionalized metal nanowires and a second regioncomprising the oxidative state or salt of the same metal in the firstregion.

In one embodiment of the present invention, the method of patterning the

conductive film comprisesproviding a substrate,forming a film comprising a first region having metal nanowires, whereinat least some of metal nanowires are surface functionalized and inert tooxidation or acid reactions;evaporating away the solvent in the metal nanowire film;exposing the nanowire film to a chemical reagent;converting the metal in the metal nanowire network to its oxidativestate and forming a second region,wherein the first and second region have different electricalproperties, but having substantially same or similar optical properties,with difference in refractive indexes are less than 0.2, and thedifference in haze is no more than 0.2%.

In one embodiment of the present invention, the method of patterning the

conductive film comprisesproviding a substrate,forming a film comprising a surface functionalized silver nanowirewherein some portion of the nanowire is surface functionalized and inertto oxidation or etching,exposing the film to etchants or oxidants and reacting the nanowire withoxidants/acids, disintegrating the unprotected non-surfacefunctionalized nanowire into segments;wherein the arrangement of surface functionalized portions andnon-surface functionalized portions on a nanowire can be regularly orrandomly pitched.The randomly pitched non-surface functionalized area can occur ascoverage defects or insufficient coverage of surface molecule assemblyon nanowires.

Post Treatment of the Patterned Transparent Conductive Film

After the transparent conductive film is patterned into desiredconductive regions and non conductive regions, the application of heatmay also be used at this point as a post-treatment. Typically, thepatterned transparent conductive film exposed to anywhere from 80° C. to250° C. for up to 10 min, and more preferably is exposed to anywherefrom 100° C. to 160° C. for anywhere from about 10 seconds to 2 minutes.The transparent conductive film can also be exposed to temperatureshigher than 250° C. and can be even higher, depending on the type ofsubstrate. For example, glass substrate can be heat-treated at atemperature range of about 350° C. to 400° C. However, post treatmentsat higher temperatures (e.g., higher than 250° C.) require the presenceof a non-oxidative atmosphere, such as nitrogen.

In another examples, an infrared lamp could be used as eitherindependently or together with the heating method to anneal thepatterned transparent film. Again, the post anneal is recommended toperform in an inert atmosphere.

Other Functional Layers

The patterned conductive film can further comprise other functionallayers, in order to meet end use applications. Other functional layersinclude an adhesive layer, anti-reflective layer, anti-glare layer,barrier layers, hard coats, and protective films. These other functionallayers are employed sometimes to enhance the overall optical performanceand improve the mechanical properties of the transparent conductivefilm. These additional layers, also referred to as“performance-enhancing layers”, can be one or more anti-reflectivelayers, anti-glare layers, adhesive layers, barrier layers, and hardcoats. In certain embodiments, one performance-enhancing layer providesmultiple benefits. For example, an anti-reflective layer can alsofunction as a hard coat mod/ora barrier layer. In addition to theirspecific properties, the performance-enhancing layers are opticallyclear.

“Anti-reflective layer” refers to a layer that can reduce reflectionloss at a reflective surface of the transparent conductive film. Theanti-reflective layer can therefore be positioned on the outer surfacesof the transparent conductive film. Materials suitable asanti-reflective layers are well known in the art, including withoutlimitation: fluoropolymers, fluoropolymer blends or copolymers, at about100 nm thick or 200 nm in thickness.

“Anti-glare layer” refers to a layer that reduces unwanted reflection atan outer surface of the transparent conductive film by providing fineroughness on the surface to scatter the reflection. Suitable anti-glarematerials are well known in the art, including without limitation,siloxanes, polystyrene/PMMA blend, lacquer (e.g., butylacetate/nitrocellulose/wax/alkyd resin), polythiophenes, polypyrroles,polyurethane, nitrocellulose, and acrylates, all of which may comprise alight diffusing material such as colloidal or fumed silica. Blends andcopolymers of these materials can have microscale compositionalheterogeneities, which can also exhibit light diffusion behavior toreduce glare.

“Hard coat”, or “anti-abrasion layer” refers to a coating that providesadditional surface protection against scratches and abrasion. Examplesof suitable hard coats include synthetic polymers such as polyacrylics,epoxy, polyurethanes, polysilanes, silicones, poly(silico-acrylic) andso on. Typically, the hard coat also comprises colloidal silica. Thethickness of the hard coat is typically from about 1 to 50 μm.

“Adhesive layer” refers to any optically clear material that bonds twoadjacent layers (e.g., conductive layer and substrate) together withoutaffecting the physical, electrical or optical properties of eitherlayer. Optically clear adhesive material are well known in the art,including without limitation: acrylic resins, chlorinated olefin resins,resins of vinyl chloride-vinyl acetate copolymer, maleic acid resins,chlorinated rubber resins, cyclorubber resins, polyamide resins,cumarone indene resins, resins of ethylene-vinyl acetate copolymer,polyester resins, urethane resins, styrene resins, polysiloxanes and thelike.

“Barrier layer” refers to a layer that reduces or prevents gas or fluidpermeation into the transparent conductive film. It has been shown thatcorroded metal nanowires can cause a significant decrease in theelectrical conductivity as well as the light transmission of theconductive layer. The barrier layer can effectively inhibit atmosphericcorrosive gas from entering the conductive layer and contacting themetal nanowires in the matrix. The barrier layers are well known in theart, including without limitation: see, e.g. U.S. Patent Application No.2004/0253463, U.S. Pat. Nos. 5,560,998 and 4,927,689, EP Patent No.132,565, and JP Patent No. 57,061,025. Moreover, any of theanti-reflective layer, anti-glare layer and the hard coat can also actas a barrier layer.

In certain embodiments, the patterned transparent conductive film mayfurther comprise a protective film above the conductive layer (the layercomprise metal nanowires). The protective film is typically flexible andcan be made of the same material as the flexible substrate. Examples ofprotective film include, but are not limited to: polyester, polyethyleneterephthalate (PET), polybutylene terephthalate, polymethyl methacrylate(PMMA), acrylic resin, polycarbonate (PC), polystyrene, or the like;particularly preferable is PET, PC, PMMA, or TAC because of their highstrength.

In Devices

The patterned transparent conductive films as described herein can beused as films in a wide variety of devices, including any device thatcurrently makes use of transparent conductive films such as metal oxidefilms. Examples of suitable devices include flat panel displays, LCDs,touch screens, electomagnetic shieldings, functional glasses (e.g., forelectrochromic windows), optoelectronic devices, and the like. Inaddition, the transparent conductive herein can be used in flexibledevices, such as flexible displays and touch screens.

Example 1 Synthesis of Silver Nanowires

51 g of PVP is first dissolved in 500 mL of glycerol solvent and heatedto 15° C. In the meantime, 51 g of silver nitrate is dissolved in 300 mlof glycerol separately to form silver nitrate solution. Then, the silvernitrate solution is added to the PVP solution at a constant rate of 20ml/min for 9 minutes; this is then followed by adding the remainingportion of silver nitrate solution at 4 ml/min for another 30 minutes.The reaction is allowed to proceed for another 3 hours before it isquenched by mixing equal volume of cold water (20 C). The reactionmixture was then solvent exchanged by repeated centrifuge andre-dispersion in desired solvents. Choices of solvent for thecentrifuge/re-dispersion processes is determined by the desireddispersing medium for nanowire in ink formulation, e.g. water orethanol. Typical amount of solvent used in re-dispersion is about 50× ormore of the remaining solid collected by centrifuged. The whole processis repeated at least 3 times.

Example 2 Preparation of a Transparent Conductive Film

Silver nanowires (25 um, 60 nm) were first prepared by polyol processand followed by purification. Then 0.15 g of purified nanowires wasdispersed in a 50 ml of binder free solvent such as ethanol or methanolor IPA to prepare a 0.3% w/v of silver nanowire dispersion.

On a PET substrate, a thin layer of SNW dispersion is spun coated at1500 rpm spin speed for 30 s. The coated substrate was baked at 100 Cfor 1 minute. A layer of 1.8% wt silica sol-gel solution was applied ontop of baked sample by spin coating at 2500 rpm for 10 s. The resultedsample was further baked at 100 C for 1 minute.

The final sample comprises a PET substrate with a connected silvernanowire network buried or embedded in closely packed silica particles.

Examples of Patterning of Conductive Layers by Inkjet Printing

Prepare etching solution and place the solution into ink containers ofthe inkjet printing cartridges. Adjust the inkjet printer to appropriatevalues, select a desired pattern to be printed and lay differentpatterns on top of each other if necessary to achieve accurate patterns.FIG. 10 illustrates an exemplary patterns, wherein the white linesrepresent where the printing lines of the etchant. Appropriate heat isapplied when necessary.

FIG. 11 shows a SEM image where the second regions were all etched away.FIG. 12 shows a SEM image wherein the second region is oxidized insteadof all etched way. Comparing FIG. 12 with FIG. 11, FIG. 12 shows clearlythat patterned film is more optically uniform.

FIG. 13 a is an SEM image showing the conductive film comprising surfacefunctionalize metal nanowires after being patterned, wherein the area102 is the first area, not being etched, and area 106 is the secondarea, being etched. The first area 102 is the conductive area and thesecond area 106 is the non-conductive area. FIG. 13 b is a zoom in imageof part of FIG. 13 a. FIG. 13 b demonstrated that the non-conductiveregions comprise shorter metal nanowires, or less metal nanowires, ormore isolated nanowire clusters.

It will be appreciated by those skilled in the art that the abovediscussion is for demonstration purpose; and the examples discussedabove are some of many possible examples. Other variations are alsoapplicable. Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to affect such feature, structure, orcharacteristic in connection with other ones of the embodiments.Furthermore, for ease of understanding, certain method procedures mayhave been delineated as separate procedures; however, these separatelydelineated procedures should not be construed as necessarily orderdependent in their performance. That is, some procedures may be able tobe performed in an alternative ordering, simultaneously, etc. Inaddition, exemplary diagrams illustrate various methods in accordancewith embodiments of the present disclosure. Such exemplary methodembodiments are described herein using and can be applied tocorresponding apparatus embodiments, however, the method embodiments arenot intended to be limited thereby. Although few embodiments of thepresent invention have been illustrated and described, it would beappreciated by those skilled in the art that changes may be made inthese embodiments without departing from the principles and spirit ofthe invention. The foregoing embodiments are therefore to be consideredin all respects illustrative rather than limiting on the inventiondescribed herein. Scope of the invention is thus indicated by theappended claims rather than by the foregoing description, and allchanges, which come within the meaning and range of equivalency of theclaims, are intended to be embraced therein. As used in this disclosure,the term “preferably” is non-exclusive and means “preferably, but notlimited to.” Terms in the claims should be given their broadestinterpretation consistent with the general inventive concept as setforth in this description. For example, the terms “coupled” and“connect” (and derivations thereof) are used to connote both direct andindirect connections/couplings. As another example, “having” and“including”, derivatives thereof and similar transitional terms orphrases are used synonymously with “comprising” (i.e., all areconsidered “open ended” terms)—only the phrases “consisting of” and“consisting essentially of” should be considered as “close ended”.Claims are not intended to be interpreted under 112 sixth paragraphunless the phrase “means for” and an associated function appear in aclaim and the claim fails to recite sufficient structure to perform suchfunction.

1. A method for making a nanowire-based electrode having homogenousoptical property and heterogeneous electrical property. The method ofmaking a nanowire based conductive electrode comprises 1) providing asubstrate, 2) coating a first solution comprising a first material on tothe substrate to form a layer of nanowire network; 3) evaporating toremove the solvent in the metal nanowire film; 4) printing a secondsolution comprising a chemical reagent on top of the formed metalnanowire network layer; 5) heating and drying to remove the solvent inthe second solution; and 6) oxidizing the first material into a secondmaterial by the chemical reagent, wherein the first material and secondmaterial has a refractive index difference less than 0.05 and secondmaterial is less conductive than the first material.
 2. The method ofclaim 1, wherein the chemical reagent is an acid or an oxidizing agent.3. The method of claim 1, wherein the first material is silver metal. 4.The method of claim 3, wherein the second material is a silver oxide orsilver salts.
 5. The method of claim 1, wherein the second solution isprinted by an inkjet printing method.
 6. The method of claim 1, whereinthe second solution is printed according to a predetermined pattern. 7.The method of claim 1, wherein the second region has one dimension lessthan 50 um.
 8. The method of claim 1, wherein the first region has onedimension larger than 1 um.
 9. The method of claim 1, wherein thesubstrate is a flexible substrate.
 10. The method of claim 1, whereinthe substrate is a glass substrate.
 11. The method of claim 1, whereinthe nanowire in the first region has a diameter less than 50 nm.
 12. Themethod of claim 1, wherein the second solution is printed by an inkjetprinting method.
 13. The method of claim 1, wherein the second solutionis printed by roll to roll printing or sheet-by-sheet method
 14. Themethod of claim 1, wherein the resistivity ratio between the first andsecond region is over 1000 times.
 15. A method for making ananowire-based electrode having homogenous optical property andheterogeneous electrical property, comprising 1) providing a substrate,2) coating a first solution comprising a first material on to thesubstrate to form a layer of nanowire network; 3) evaporating to removethe solvent in the metal nanowire film; 4) printing a second solutioncomprising a chemical reagent on top of the formed nanowire networklayer; 5) heating and drying to remove the solvent in the secondsolution; and 6) reducing the first material into a second material bythe chemical reagent, wherein the first material and second material hasa refractive index difference less than 0.05 and second material is moreconductive than the first material.
 16. The method of claim 15, whereinthe first material is a silver oxide or any silver salt precursor. 17.The method of claim 15, wherein the second material is a silver metal.